[PATCH v5 05/15] mm/frame-vector: Use FOLL_LONGTERM
Daniel Vetter
daniel.vetter at ffwll.ch
Fri Oct 30 14:37:52 UTC 2020
On Fri, Oct 30, 2020 at 3:11 PM Tomasz Figa <tfiga at chromium.org> wrote:
>
> On Fri, Oct 30, 2020 at 11:08 AM Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> >
> > This is used by media/videbuf2 for persistent dma mappings, not just
> > for a single dma operation and then freed again, so needs
> > FOLL_LONGTERM.
> >
> > Unfortunately current pup_locked doesn't support FOLL_LONGTERM due to
> > locking issues. Rework the code to pull the pup path out from the
> > mmap_sem critical section as suggested by Jason.
> >
> > By relying entirely on the vma checks in pin_user_pages and follow_pfn
> > (for vm_flags and vma_is_fsdax) we can also streamline the code a lot.
> >
> > Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> > Cc: Jason Gunthorpe <jgg at ziepe.ca>
> > Cc: Pawel Osciak <pawel at osciak.com>
> > Cc: Marek Szyprowski <m.szyprowski at samsung.com>
> > Cc: Kyungmin Park <kyungmin.park at samsung.com>
> > Cc: Tomasz Figa <tfiga at chromium.org>
> > Cc: Mauro Carvalho Chehab <mchehab at kernel.org>
> > Cc: Andrew Morton <akpm at linux-foundation.org>
> > Cc: John Hubbard <jhubbard at nvidia.com>
> > Cc: Jérôme Glisse <jglisse at redhat.com>
> > Cc: Jan Kara <jack at suse.cz>
> > Cc: Dan Williams <dan.j.williams at intel.com>
> > Cc: linux-mm at kvack.org
> > Cc: linux-arm-kernel at lists.infradead.org
> > Cc: linux-samsung-soc at vger.kernel.org
> > Cc: linux-media at vger.kernel.org
> > Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> > --
> > v2: Streamline the code and further simplify the loop checks (Jason)
> >
> > v5: Review from Tomasz:
> > - fix page counting for the follow_pfn case by resetting ret
> > - drop gup_flags paramater, now unused
> > ---
> > .../media/common/videobuf2/videobuf2-memops.c | 3 +-
> > include/linux/mm.h | 2 +-
> > mm/frame_vector.c | 53 ++++++-------------
> > 3 files changed, 19 insertions(+), 39 deletions(-)
> >
>
> Thanks, looks good to me now.
>
> Acked-by: Tomasz Figa <tfiga at chromium.org>
>
> From reading the code, this is quite unlikely to introduce any
> behavior changes, but just to be safe, did you have a chance to test
> this with some V4L2 driver?
Nah, unfortunately not.
-Daniel
>
> Best regards,
> Tomasz
>
> > diff --git a/drivers/media/common/videobuf2/videobuf2-memops.c b/drivers/media/common/videobuf2/videobuf2-memops.c
> > index 6e9e05153f4e..9dd6c27162f4 100644
> > --- a/drivers/media/common/videobuf2/videobuf2-memops.c
> > +++ b/drivers/media/common/videobuf2/videobuf2-memops.c
> > @@ -40,7 +40,6 @@ struct frame_vector *vb2_create_framevec(unsigned long start,
> > unsigned long first, last;
> > unsigned long nr;
> > struct frame_vector *vec;
> > - unsigned int flags = FOLL_FORCE | FOLL_WRITE;
> >
> > first = start >> PAGE_SHIFT;
> > last = (start + length - 1) >> PAGE_SHIFT;
> > @@ -48,7 +47,7 @@ struct frame_vector *vb2_create_framevec(unsigned long start,
> > vec = frame_vector_create(nr);
> > if (!vec)
> > return ERR_PTR(-ENOMEM);
> > - ret = get_vaddr_frames(start & PAGE_MASK, nr, flags, vec);
> > + ret = get_vaddr_frames(start & PAGE_MASK, nr, vec);
> > if (ret < 0)
> > goto out_destroy;
> > /* We accept only complete set of PFNs */
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index ef360fe70aaf..d6b8e30dce2e 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -1765,7 +1765,7 @@ struct frame_vector {
> > struct frame_vector *frame_vector_create(unsigned int nr_frames);
> > void frame_vector_destroy(struct frame_vector *vec);
> > int get_vaddr_frames(unsigned long start, unsigned int nr_pfns,
> > - unsigned int gup_flags, struct frame_vector *vec);
> > + struct frame_vector *vec);
> > void put_vaddr_frames(struct frame_vector *vec);
> > int frame_vector_to_pages(struct frame_vector *vec);
> > void frame_vector_to_pfns(struct frame_vector *vec);
> > diff --git a/mm/frame_vector.c b/mm/frame_vector.c
> > index 10f82d5643b6..f8c34b895c76 100644
> > --- a/mm/frame_vector.c
> > +++ b/mm/frame_vector.c
> > @@ -32,13 +32,12 @@
> > * This function takes care of grabbing mmap_lock as necessary.
> > */
> > int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
> > - unsigned int gup_flags, struct frame_vector *vec)
> > + struct frame_vector *vec)
> > {
> > struct mm_struct *mm = current->mm;
> > struct vm_area_struct *vma;
> > int ret = 0;
> > int err;
> > - int locked;
> >
> > if (nr_frames == 0)
> > return 0;
> > @@ -48,40 +47,26 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
> >
> > start = untagged_addr(start);
> >
> > - mmap_read_lock(mm);
> > - locked = 1;
> > - vma = find_vma_intersection(mm, start, start + 1);
> > - if (!vma) {
> > - ret = -EFAULT;
> > - goto out;
> > - }
> > -
> > - /*
> > - * While get_vaddr_frames() could be used for transient (kernel
> > - * controlled lifetime) pinning of memory pages all current
> > - * users establish long term (userspace controlled lifetime)
> > - * page pinning. Treat get_vaddr_frames() like
> > - * get_user_pages_longterm() and disallow it for filesystem-dax
> > - * mappings.
> > - */
> > - if (vma_is_fsdax(vma)) {
> > - ret = -EOPNOTSUPP;
> > - goto out;
> > - }
> > -
> > - if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
> > + ret = pin_user_pages_fast(start, nr_frames,
> > + FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM,
> > + (struct page **)(vec->ptrs));
> > + if (ret > 0) {
> > vec->got_ref = true;
> > vec->is_pfns = false;
> > - ret = pin_user_pages_locked(start, nr_frames,
> > - gup_flags, (struct page **)(vec->ptrs), &locked);
> > - goto out;
> > + goto out_unlocked;
> > }
> >
> > + mmap_read_lock(mm);
> > vec->got_ref = false;
> > vec->is_pfns = true;
> > + ret = 0;
> > do {
> > unsigned long *nums = frame_vector_pfns(vec);
> >
> > + vma = find_vma_intersection(mm, start, start + 1);
> > + if (!vma)
> > + break;
> > +
> > while (ret < nr_frames && start + PAGE_SIZE <= vma->vm_end) {
> > err = follow_pfn(vma, start, &nums[ret]);
> > if (err) {
> > @@ -92,17 +77,13 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
> > start += PAGE_SIZE;
> > ret++;
> > }
> > - /*
> > - * We stop if we have enough pages or if VMA doesn't completely
> > - * cover the tail page.
> > - */
> > - if (ret >= nr_frames || start < vma->vm_end)
> > + /* Bail out if VMA doesn't completely cover the tail page. */
> > + if (start < vma->vm_end)
> > break;
> > - vma = find_vma_intersection(mm, start, start + 1);
> > - } while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP));
> > + } while (ret < nr_frames);
> > out:
> > - if (locked)
> > - mmap_read_unlock(mm);
> > + mmap_read_unlock(mm);
> > +out_unlocked:
> > if (!ret)
> > ret = -EFAULT;
> > if (ret > 0)
> > --
> > 2.28.0
> >
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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